The present invention relates generally to overload relays for electromagnetic contactors, and more particularly to a control system for controlling the coil in an electromagnetic motor starter that uses an 8-pin, 8-bit microcontroller and I/O reduction circuitry to process at least 13 I/O's and calculate the operating temperature of a motor on a real-time basis.
In typical electromagnetic contactors, an overload relay is used to protect a particular load, such as a motor, from excess current and heat. Known overload relays incorporate bi-metal switches which require hand bending and tweaking to calibrate for a particular device. Needless to say, accuracy is suspect after field adjustments are made, such as once the full load amperage (FLA) adjustment is made. Further, such bi-metal switches and heaters used in existing overload relays, are typically connected in series with the contacts of a contactor. These bi-metal devices therefore require separate invasive connections between the contactor and overload relay, and not only increase the cost and size of the starter, but also the manufacturability of the device.
Another problem with such known electromagnetic overload relays is the use of current measurement devices such as current transformers and torroids. Current transformers are large and bulky, thereby adding to the overall size and cost of the device. Torroids are not as large, but still add to the size and expense of the package, and offer limited accuracy and range.
Therefore, it would be desirable to have a motor overload coil control capable of using the relatively tiny Hall effect sensors which have a much wider dynamic range for sensing current. Further, it would be desirable to have such a device that eliminates the need for the mechanical bi-metal switches.